[libc++][TZDB] Finishes zoned_time member functions.

Note the implementation of
  zoned_time& operator=(const local_time<Duration>& lt);
is not correct; however the wording cannot be easily implemented. It could
be if the object caches the local_time assigned. However this does not
seem to intended. The current implementation matches MSVC STL and
libstdc++.

Implements parts of:
- P0355 Extending to chrono Calendars and Time Zones

Author: mordante

libcxx/include/__chrono/zoned_time.h

@@ -146,8 +146,29 @@ class zoned_time {
     } && is_convertible_v<sys_time<_Duration2>, sys_time<_Duration>>)
       : zoned_time{__traits::locate_zone(__name), __zt, __c} {}
 
+  _LIBCPP_HIDE_FROM_ABI zoned_time& operator=(const sys_time<_Duration>& __tp) {
+    __tp_ = __tp;
+    return *this;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI zoned_time& operator=(const local_time<_Duration>& __tp) {
+    // TODO TZDB This seems wrong.
+    // Assigning a non-existant or abiguous time will throw and not satisfy
+    // the post condition. This seems quite odd; I constructed an object with
+    // choose::earliest and that choice is not respected.
+    // what did LEWG do with this.
+    // MSVC STL and libstdc++ behave the same
+    __tp_ = __zone_->to_sys(__tp);
+    return *this;
+  }
+
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI operator sys_time<duration>() const { return get_sys_time(); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI explicit operator local_time<duration>() const { return get_local_time(); }
+
   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI _TimeZonePtr get_time_zone() const { return __zone_; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI local_time<duration> get_local_time() const { return __zone_->to_local(__tp_); }
   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI sys_time<duration> get_sys_time() const { return __tp_; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI sys_info get_info() const { return __zone_->get_info(__tp_); }
 
 private:
   _TimeZonePtr __zone_;

libcxx/test/libcxx/diagnostics/chrono.nodiscard.verify.cpp

@@ -81,7 +81,15 @@ void test() {
 
   {
     std::chrono::zoned_time<std::chrono::seconds> zt;
-    zt.get_time_zone(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
-    zt.get_sys_time();  // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+    // expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    static_cast<std::chrono::sys_seconds>(zt);
+    // expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    static_cast<std::chrono::local_seconds>(zt);
+
+    zt.get_time_zone();  // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+    zt.get_local_time(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+    zt.get_sys_time();   // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+    zt.get_info();       // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
   }
 }

libcxx/test/std/time/time.zone/time.zone.zonedtime/time.zone.zonedtime.members/assign.local_time.pass.cpp

@@ -0,0 +1,245 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: no-filesystem, no-localization, no-tzdb
+
+// XFAIL: libcpp-has-no-experimental-tzdb
+// XFAIL: availability-tzdb-missing
+
+// <chrono>
+
+// template<class Duration, class TimeZonePtr = const time_zone*>
+// class zoned_time;
+//
+// zoned_time& operator=(const local_time<Duration>& st);
+
+// TODO TZDB Investigate the issues in this test, this seems like
+// a design issue of the class.
+//
+// [time.zone.zonedtime.members]/3
+//   Effects: After assignment, get_local_time() == lt.
+//   This assignment has no effect on the return value of get_time_zone().
+//
+// The test cases describe the issues.
+
+#include <cassert>
+#include <chrono>
+#include <concepts>
+#include <type_traits>
+
+// Tests unique conversions. To make sure the test is does not depend on changes
+// in the database it uses a time zone with a fixed offset.
+static void test_unique() {
+  // common_type_t<duration, seconds> -> duration
+  {
+    using duration         = std::chrono::nanoseconds;
+    using sys_time_point   = std::chrono::sys_time<duration>;
+    using local_time_point = std::chrono::local_time<duration>;
+    using zoned_time       = std::chrono::zoned_time<duration>;
+    zoned_time zt{"Etc/GMT+1", sys_time_point{duration{42}}};
+
+    assert(zt.get_time_zone() == std::chrono::locate_zone("Etc/GMT+1"));
+    assert(zt.get_sys_time() == sys_time_point{duration{42}});
+    assert(zt.get_local_time() == local_time_point{duration{42} - std::chrono::hours{1}});
+
+    std::same_as<zoned_time&> decltype(auto) _ = zt = local_time_point{duration{99}};
+    assert(zt.get_time_zone() == std::chrono::locate_zone("Etc/GMT+1"));
+    assert(zt.get_sys_time() == sys_time_point{duration{99} + std::chrono::hours{1}});
+    assert(zt.get_local_time() == local_time_point{duration{99}});
+  }
+  {
+    using duration         = std::chrono::microseconds;
+    using sys_time_point   = std::chrono::sys_time<duration>;
+    using local_time_point = std::chrono::local_time<duration>;
+    using zoned_time       = std::chrono::zoned_time<duration>;
+    zoned_time zt{"Etc/GMT+1", sys_time_point{duration{42}}};
+
+    assert(zt.get_time_zone() == std::chrono::locate_zone("Etc/GMT+1"));
+    assert(zt.get_sys_time() == sys_time_point{duration{42}});
+    assert(zt.get_local_time() == local_time_point{duration{42} - std::chrono::hours{1}});
+
+    std::same_as<zoned_time&> decltype(auto) _ = zt = local_time_point{duration{99}};
+    assert(zt.get_time_zone() == std::chrono::locate_zone("Etc/GMT+1"));
+    assert(zt.get_sys_time() == sys_time_point{duration{99} + std::chrono::hours{1}});
+    assert(zt.get_local_time() == local_time_point{duration{99}});
+  }
+  {
+    using duration         = std::chrono::milliseconds;
+    using sys_time_point   = std::chrono::sys_time<duration>;
+    using local_time_point = std::chrono::local_time<duration>;
+    using zoned_time       = std::chrono::zoned_time<duration>;
+    zoned_time zt{"Etc/GMT+1", sys_time_point{duration{42}}};
+
+    assert(zt.get_time_zone() == std::chrono::locate_zone("Etc/GMT+1"));
+    assert(zt.get_sys_time() == sys_time_point{duration{42}});
+    assert(zt.get_local_time() == local_time_point{duration{42} - std::chrono::hours{1}});
+
+    std::same_as<zoned_time&> decltype(auto) _ = zt = local_time_point{duration{99}};
+    assert(zt.get_time_zone() == std::chrono::locate_zone("Etc/GMT+1"));
+    assert(zt.get_sys_time() == sys_time_point{duration{99} + std::chrono::hours{1}});
+    assert(zt.get_local_time() == local_time_point{duration{99}});
+  }
+  // common_type_t<seconds, seconds> -> seconds
+  {
+    using duration         = std::chrono::seconds;
+    using sys_time_point   = std::chrono::sys_time<duration>;
+    using local_time_point = std::chrono::local_time<duration>;
+    using zoned_time       = std::chrono::zoned_time<duration>;
+    zoned_time zt{"Etc/GMT+1", sys_time_point{duration{42}}};
+
+    assert(zt.get_time_zone() == std::chrono::locate_zone("Etc/GMT+1"));
+    assert(zt.get_sys_time() == sys_time_point{duration{42}});
+    assert(zt.get_local_time() == local_time_point{duration{42} - std::chrono::hours{1}});
+
+    std::same_as<zoned_time&> decltype(auto) _ = zt = local_time_point{duration{99}};
+    assert(zt.get_time_zone() == std::chrono::locate_zone("Etc/GMT+1"));
+    assert(zt.get_sys_time() == sys_time_point{duration{99} + std::chrono::hours{1}});
+    assert(zt.get_local_time() == local_time_point{duration{99}});
+  }
+  // common_type_t<duration, seconds> -> seconds
+  {
+    using duration         = std::chrono::days;
+    using sys_time_point   = std::chrono::sys_time<duration>;
+    using local_time_point = std::chrono::local_time<duration>;
+    using zoned_time       = std::chrono::zoned_time<duration>;
+    zoned_time zt{"Etc/GMT+1", sys_time_point{duration{42}}};
+
+    assert(zt.get_time_zone() == std::chrono::locate_zone("Etc/GMT+1"));
+    assert(zt.get_sys_time() == std::chrono::sys_seconds{duration{42}});
+    assert(zt.get_local_time() == std::chrono::local_seconds{duration{42} - std::chrono::hours{1}});
+
+    std::same_as<zoned_time&> decltype(auto) _ = zt = local_time_point{duration{99}};
+    assert(zt.get_time_zone() == std::chrono::locate_zone("Etc/GMT+1"));
+    assert(zt.get_sys_time() == std::chrono::sys_seconds{duration{99} + std::chrono::hours{1}});
+    assert(zt.get_local_time() == std::chrono::local_seconds{duration{99}});
+  }
+  {
+    using duration         = std::chrono::weeks;
+    using sys_time_point   = std::chrono::sys_time<duration>;
+    using local_time_point = std::chrono::local_time<duration>;
+    using zoned_time       = std::chrono::zoned_time<duration>;
+    zoned_time zt{"Etc/GMT+1", sys_time_point{duration{42}}};
+
+    assert(zt.get_time_zone() == std::chrono::locate_zone("Etc/GMT+1"));
+    assert(zt.get_sys_time() == std::chrono::sys_seconds{duration{42}});
+    assert(zt.get_local_time() == std::chrono::local_seconds{duration{42} - std::chrono::hours{1}});
+
+    std::same_as<zoned_time&> decltype(auto) _ = zt = local_time_point{duration{99}};
+    assert(zt.get_time_zone() == std::chrono::locate_zone("Etc/GMT+1"));
+    assert(zt.get_sys_time() == std::chrono::sys_seconds{duration{99} + std::chrono::hours{1}});
+    assert(zt.get_local_time() == std::chrono::local_seconds{duration{99}});
+  }
+  /* This does not work; due to using __tp_ = __zone_->to_sys(__tp);
+   * Here the ambiguous/non-existent exception can't stream months and years,
+   * leading to a compilation error.
+  {
+    using duration         = std::chrono::months;
+    using sys_time_point   = std::chrono::sys_time<duration>;
+    using local_time_point = std::chrono::local_time<duration>;
+    using zoned_time       = std::chrono::zoned_time<duration>;
+    zoned_time zt{"Etc/GMT+1", sys_time_point{duration{42}}};
+
+    assert(zt.get_time_zone() == std::chrono::locate_zone("Etc/GMT+1"));
+    assert(zt.get_sys_time() == std::chrono::sys_seconds{duration{42}});
+    assert(zt.get_local_time() == std::chrono::local_seconds{duration{42} - std::chrono::hours{1}});
+
+    std::same_as<zoned_time&> decltype(auto) _ = zt = local_time_point{duration{99}};
+    assert(zt.get_time_zone() == std::chrono::locate_zone("Etc/GMT+1"));
+    assert(zt.get_sys_time() == std::chrono::sys_seconds{duration{99} + std::chrono::hours{1}});
+    assert(zt.get_local_time() == std::chrono::local_seconds{duration{99}});
+  } */
+}
+
+// Tests non-existant conversions.
+static void test_nonexistent() {
+  using namespace std::literals::chrono_literals;
+
+  const std::chrono::time_zone* tz = std::chrono::locate_zone("Europe/Berlin");
+
+  // Z Europe/Berlin 0:53:28 - LMT 1893 Ap
+  // ...
+  // 1 DE CE%sT 1980
+  // 1 E CE%sT
+  //
+  // ...
+  // R E 1981 ma - Mar lastSu 1u 1 S
+  // R E 1996 ma - O lastSu 1u 0 -
+
+  // Pick an historic date where it's well known what the time zone rules were.
+  // This makes it unlikely updates to the database change these rules.
+  std::chrono::local_time<std::chrono::seconds> time{
+      (std::chrono::sys_days{std::chrono::March / 30 / 1986} + 2h + 30min).time_since_epoch()};
+
+  using duration         = std::chrono::seconds;
+  using sys_time_point   = std::chrono::sys_time<duration>;
+  using local_time_point = std::chrono::local_time<duration>;
+  using zoned_time       = std::chrono::zoned_time<duration>;
+  zoned_time zt{tz};
+
+#ifndef TEST_NOEXCEPT
+  bool thrown = false;
+  try {
+    std::same_as<zoned_time&> decltype(auto) _ = zt = time;
+  } catch (const std::chrono::nonexistent_local_time&) {
+    thrown = true;
+  }
+  // There is no system type that can represent the current local time. So the
+  // assertion passes. The current implementation throws an exception too.
+  assert(zt.get_local_time() != time);
+  assert(thrown);
+#endif
+}
+
+// Tests ambiguous conversions.
+static void test_ambiguous() {
+  using namespace std::literals::chrono_literals;
+
+  const std::chrono::time_zone* tz = std::chrono::locate_zone("Europe/Berlin");
+
+  // Z Europe/Berlin 0:53:28 - LMT 1893 Ap
+  // ...
+  // 1 DE CE%sT 1980
+  // 1 E CE%sT
+  //
+  // ...
+  // R E 1981 ma - Mar lastSu 1u 1 S
+  // R E 1996 ma - O lastSu 1u 0 -
+
+  // Pick an historic date where it's well known what the time zone rules were.
+  // This makes it unlikely updates to the database change these rules.
+  std::chrono::local_time<std::chrono::seconds> time{
+      (std::chrono::sys_days{std::chrono::September / 28 / 1986} + 2h + 30min).time_since_epoch()};
+
+  using duration         = std::chrono::seconds;
+  using sys_time_point   = std::chrono::sys_time<duration>;
+  using local_time_point = std::chrono::local_time<duration>;
+  using zoned_time       = std::chrono::zoned_time<duration>;
+  zoned_time zt{tz};
+
+#ifndef TEST_NOEXCEPT
+  bool thrown = false;
+  try {
+    std::same_as<zoned_time&> decltype(auto) _ = zt = time;
+  } catch (const std::chrono::ambiguous_local_time&) {
+    thrown = true;
+  }
+  // There is no system type that can represent the current local time. So the
+  // assertion passes. The current implementation throws an exception too.
+  assert(zt.get_local_time() != time);
+  assert(thrown);
+#endif
+}
+
+int main(int, char**) {
+  test_unique();
+  test_nonexistent();
+  test_ambiguous();
+
+  return 0;
+}